1. Field of the Invention
The present invention relates to a method for melting semiconductor wafer raw material, in which the semiconductor wafer raw material is placed in a crucible of a single crystal manufacturing apparatus, and is melted by heating the crucible with a side heater, and particularly relates to a melting method for semiconductor wafer raw material that uses a side heater to heat the crucible bottom part to reduce the amount of gas bubbles in the melt.
2. Description of the Related Art
To manufacture the single crystal silicon using the single crystal manufacturing device, chunks of polycrystalline as raw material are put into the quartz crucible. The side surface of the crucible is then heated using the side heater that is arranged so as to surround the side of the crucible. As the material has been melted, the silicon melt is generated. On the tip of a crystal pulling mechanism disposed in an upper part of the crucible, a silicon seed crystal is disposed. After being dipped into the silicon melt, the seed crystal is pulled up while being rotated around the pulling up axis. The silicon is then deposited in accordance with the crystal orientation of the seed crystal, whereby the ingot of the single crystal silicon can be formed.
From the ingot of the single crystal silicon, wafers are cut. However, those cut wafers may have bubble-shaped defects, which is called the pinhole defect. This pinhole defect occurs when bubbles existed in the melt are incorporated into the single crystal silicon, and is considered to be caused by the bubble existed on the surface of the inner wall of the crucible, SiO gas attached to the raw material, and the like, at the time of melt of the raw material.
It should be noted that the Japanese Patent Application Laid-Open No. 05-9097 (Patent Literature 1), and the Japanese Patent Application Laid-Open No. 2000-169287 (Patent Literature 2) disclose a technique in which the pinhole defects are reduced using a pressure control in the furnace such as performing the melting process of the raw material under the low pressure and performing the pulling process of the ingot under the high pressure.
However, the quality of the crystal depends on the pressure in the furnace. To achieve the high quality ingot, it is necessary to accurately control the pressure in the furnace during manufacturing the ingot. Although the technique disclosed in the above Patent Literatures 1 and 2 is directed to controlling the pressure in the furnace to reduce the pinhole defects, the quality of the crystal is not taken into consideration in this technique. Accordingly, it is difficult for the technique disclosed in the above Patent Literatures 1 and 2 to achieve both improvement of the quality and reduction in the pinhole defect.
The present invention has been made in view of the above circumstances, and has an object to reduce the bubbles in the melt and pinhole defects occurring in the wafer.